THROUGH-SPACE AND THROUGH-BOND EFFECTS ON EXCITON INTERACTIONS IN RIGIDLY LINKED DINAPHTHYL MOLECULES

Electronic absorption spectra of a series of dinaphthyl molecules, in which the naphthyl moieties are separated by a rigid polynorbornyl bridge, together with a corresponding model compound have been measured in n-hexane and acetonitrile solvents. Resonance (molecular exciton) splittings of the naphthalene 1A(g) --> 2(1)B3u electronic transition are observed and found to be substantially greater than predicted by the usual dipole-dipole model. For the two-bond bridged compound a description of the exciton interaction requires consideration of direct through-space orbital overlap between naphthalenes. Through-space interchromophore orbital overlaps in the four-bond and the six-bond bridged compounds are negligible, and it is concluded that for these systems a significant contribution by a through-bond interaction (involving the sigma- and sigma*-orbitals of the bridge) leads to the efficient delocalization of the excitation observed. This is the first evidence that exciton interactions can be enhanced by a through-bond interaction.